(a). Field of the Invention
The invention relates to communication systems, and more particularly to an apparatus and method for interference cancellation used in the communication systems.
(b). Description of the Prior Arts
In a full duplex communication system, since the transmission and reception of signals are performed simultaneously in the same channel, a transceiver will receive the signal transmitted by a remote transceiver and the echo signal transmitted by the transceiver itself. Besides, if the full duplex communication system includes multiple channels, such as the Ethernet communication system, then the receiver will further receive the cross-talk resulted from the transmitted signal within another channel. The echo and cross-talk can degrade the performance of the receiver, thus how to cancel the echo and cross-talk is very important for the communication system.
In prior arts, digital cancellation is used to cancel the echo and cross-talk. FIG. 1 is a diagram showing the architecture used in prior arts to cancel the echo and cross-talk. In FIG. 1, an analog-to-digital converter (ADC) 12 receives an analog received signal and converts it into a digital received signal. An echo/cross-talk canceller generates a cancellation signal corresponding to the echo or cross-talk, and an adder 13 subtracts the cancellation signal from the digital received signal so as to cancel the echo or cross-talk.
However, when the transmission rate of the communication system is high, the specification request for the ADC 12 is also raised. For example, a 10 Gbps Ethernet receiver requires at least 10-bit ADCs operated at the rate of at least 800 MHz, which is difficult to design and implement. In particular, the Ethernet transceiver simultaneously receives a transmitted signal from a remote transmitter and an echo signal from it's own transmitter, the power of which is much larger than that of the transmitted signal. In order to completely receive these two signals, the dynamic range and effective number of bits (ENOB) of the ADC must be large enough, but this is very difficult to design for system designers. Thus, the conventional approach to echo/cross-talk cancellation in digital domain has the drawback of severe requirement of ADC specification.